Deflecting circuit



Jan. 29, 1946. w, B wm JR 2,393,601

DEFLECTfNG CIRCUIT Filed July 30, 1942 SOURCE OF TRIGGER/N6 IMPUL SE6 .55 &

m/v /vroe M W BALDWIN JR.

ATTORNEY Patented Jan. 29, 1946 UNIT DEFLECTING ClllltiJUll'll York Application July 30, 1942, Serial No, 452,929

13 Claims.

Thls invention relates to deflecting circuits for cathode ray tubes and particularly to a circuit for and a method of supplying deflecting current to deflecting coils of a cathode ray tube from a push-pull amplifier.

For thepurpose of supplyin an amplified electric' wave to a pair of deflecting coils of a cathode ray' tube, it has been found advantageous to employ push-pull amplification in the amplifier stage which supplies energy to the coils in order to balance out second harmonic distortion.

-When, for example, the vertical deflecting coils tromotive force applied to the input circuit of the push-pull amplifier, it has been discovered that the horizontal deflection of the cathode ray beam does not follow a straight line. tortion of the scanning path was found to be due to the opposing electromagnetic fields set up in the vertical sweep coils, respectively, when energized by the anode currents of the push-pull amplifier.

For the purpose of avoiding distortion of the scanning path in accordance with the present invention, a portion of each of a pair of deflecting coils is connected in the anode circuit of one tube of a push-pull amplifier while the remaining portion of each of the pair of deflecting coils is connected in the anode circuit of the other tube of the push-pull amplifier so that, at any instant, the coils on opposite sides of the cathode ray tube, respectively, set up aiding magnetomotive forces which are preferably substantially equal. Under this condition, when the anode currents which-. energize the vertical deflecting coils, for examp e, have a certain amplitude, the electromagnetic ileld due to these coils is substantially uniform within the central region of the cathode ray tube through which the cathode ray beam is deflected horizontally.

Fig. 1 of the accompanying drawing is a dia grammatic view of a deflecting circuit for a cathode ray tube; and

Figs. 2 and 3 are diagrams to which reference will be made in describing the invention.

Referring to Fig. 1 of the drawing, there is shown a cathode ray tube which may be of any well-known type such as isemployed for scanning a field of View in the process of generating a television current or for producing images under control of a television current, for example.

This dis-- y the electrodes HI and t includes a cathode El, and anodes E2 and a source of electromotive force it for energizing l2 to cause a cathode ray beam to be generated and focussed upon a fiuorescent screen it. The intensity of the cathode ray beam may be controlled by applying a suitable potential to a control electrode 56 Two sets or pairs of deflecting coils are provided for deflecting the cathode ray beam along different coordinates, respectively, the coils l5 and it being supplied with energy from a sawtoothed wave oscillator it to cause the cathode ray beam to be deflected horizontally at a relatively high frequency and the coils 28, 2. and, 22, 23 being energized to cause the cathode ray beam to be dc flected vertically at a relati 'cly low frequency.

For generating the vertice deflecting toothed wave, there are provided. condensers and of equal capacity connected in. series which are charged at a constant by current from battery 25s through a constant current device 25 such as disclosed, for example, in Patent No. 2,244,913, granted June 1941 to W. A. Knoop. The directly connected plates of "he condens are grou i cond being charged after impulses pulses Ii :2 the desired fle ing 1m u on the c circu' 2 Acuum tube I "l discharge t 1 auodewai circuit the tube 2' 7. The saw-toothed voltages generated" across condensers 52 and l are impressed upon the cathode circuits of vacu in tubes 313 and iii, r ctively, of a push: pull amplifier, through so: ng ccnden s as and respectively. Each e of the push: amplifier me a centre e ode or grid s cathode and an anode T2. Biasing pots] is applied to the grids of vacuum tubes an from battery 3-2 and .in meter t resistors M and point of resistors 3 u the variable tsp of potentiometer is connected to ground. Battery which is shunted by condenser supplies anode current to vacuum tul. Ell through windconuectcd parallel and the the coils it nd being wound g magnet otivc forces. The t to acuum tube cox uect cl in the u "l parallel and being wound to prod motive forces. The magnet the cathode ray tube.

may be required for positioning the cathode ray beam when no deflecting saw-toothed wave is applied to the input circuit of the push-pull amplifier til, ti. This result may be realized, for example, by applying to the grid of one of the pushamplifler tubes a steady biasing potential different from that applied to the other push-pull amplifier tube.

I'he advantage of connecting the deflecting coils 20, 2| and 22, 23 in the manner shown in Fig. 1 may be understood from a consideration of Figs. 2 and 3. In Fig. 2, anode current is supplied to tube ltd of the push-pull amplifier from battery I32 through deflecting coil I20 to be positioned at one side of the cathode ray tube and anode current is supplied to tube I3I of the pushpull amplifier from battery I32 through deflecting coil I22 to be positioned on the other side of In order that a resultant deflecting field may be set up due to the cur-- rents flowing through coils I20 and I22 when a. deflecting wave is applied to tlie'input of pushpull amplifier I30, I3I as in Fig..- 1, the coils H20 and I22 must be wound in a manner .to set up opposing magnetomotive forces when energized by current from battery I132, as indicated by the arrows. When the currents which flow through coils IN and I22 are equal, for example, the coil on condensers 52 and 53, the currents in. windthe manner shown in Fig.1. In that arrange ment the magnetomotive force set up by coil 20, 2| on one side of the cathode ray tube and the magnetomotive force set up by the coil 22, 23 on the opposite side of the cathode ray tube are aiding and preferably substantially equal at any instant. As a result, the field set up by coils'20, 2| and 22, 23 is substantially uniform at any instant and the cathode ray beam is deflected horizontally along a substantially straight line due to the energization of the horizontal deflecting coils l5 and It.

The cathode ray beam is deflected vertically due to a saw-toothed deflecting wave applied to the input circuit of the push-pull amplifler30, 3i For example, when the grid of vacuum tube becomes more positive and the grid of tube 31 morenegative with respect to ground due to an increase in charge on the condensers 52 and it, the currents inwindings 20 and 22 increase and the currents in windings 2| and 23 decrease to" set up a vertical deflecting field in one direction. Similarly, when the grid of vacuum tube 3| becomes less negative and the grid of tube 30 be- I comes less positive due to a decrease in charge ings 2| and 23 increase and the currents in windings 20 and 22 decrease to set up a vertical deflecting field in the opposite direction.

If desired, of course, the horizontal deflecting coils I5, It may be energized by deflecting currents supplied thereto from a push-pull amplifier in the same manner in which the vertical deflecting coils20, 2| and 22, 23 are supplied with 35 deflecting currents, as described above.

lEIi will, set up an electromagnetic field which will deflect the cathode ray beam as it approaches that coil in one direction and the coil i2? will set' up a field which will deflect the cathode ray beam as it approaches coil l 22 in the opposite direction. This is indicated in Fig. 3 in which the coils I20 and I22 produce the vertical defiecting'fleld, the other pair of coils for deflecting the beam horizontally, such as coils I5 and it of Fig. 1, being not shown. As a result the cathode ray beam will be deflected horizontally, not along a straight line a as is desired, but will follow a curved path as shown by the line b. When the cathode ray beam is at a position :0 midway between the coils lit! and 822, as shown in Fig. 3, and when the currents through coils H26 and 922 are equal, the

resultant fleld set ,up by coils B2B and I 22 'and acting uponthe cathode ray beam is zero. As the cathode ray beam approaches coil l20 it is deflected vertically in one direction due tcthe fleld set up by coil lit and as the cathode ray beamapproaches coil I22 it is deflected vertically in the opposite direction due to the field set up by coil i2? as indicated by the line b. When the current through coil lZll is greater than the current through coil I 22, for example, the cathode ray beam will be deflected moreby the field due.

What is claimed is:

4 pair of deflecting coils on opposite sides of the cathode ray beam for producing the electromagnetic deflecting field when suitably energized, which comprises a pair of electric discharge tubes each having a control electrode, an anode and a is substantially avoided by connecting the ver- 7 tical deflecting coils to the push pull amplifier in cathode, means for. impressing upon the control electrodes of said tubes, respectively, alternatin deflecting potentials which are degrees out of phase with respect to each other, and means for supplying anode current to said discharge tubes through said deflecting coils to cause to be set up by each ofsaid coils a zero field or a relatively Weak field for determining the initial position of I said beam when the amplitude of said alternating deflecting potentials is zero, and to cause to be set up 'by said coils fields which are aiding and which simultaneously act upon said beam to move it in one direction or the other with respect to said initial position in accibrdance with the amplitude. of said alternating?defiecting potentials. r

2. in combination, means i331 generating a cathode ray beam, deflectingn eans comprising a pair of coils positioned on opposite sides of said cathode ray beam, respectively, for setting up an electromagneticfield for deflecting said cathode ray beam when suitably energized, a push-pull amplifier, and means for supplying to said-deflecting means from said push-pull amplifier electric energy for' causing said coils to set up aiding magnetomotiveiorces.

3. In combination, means for generating a cathode ray beam, means comprising a plurality of windings on opposite sides of said cathode ray beam,respectively, for setting up an electromagnetic deflecting field for said cathode ray beam when suitably energized, each of said windings having two portions which may be simultaneously differently energized, and means for supp y to said portions, respectively, of each of said windings periodically varying currents which have the same periodicity and which are opposed in phase to cause the two portions of each winding to set up opposing magnetomotive forces and to'cause said windings, respectively, to set up resultant magnetomotive forces which are aiding.

4. In combination, means for producing a cathode ray beam, a plurality of windings for setting up an electromagnetic deflecting field for said cathode ray beam when suitably energized, and means for supplying to each of said windings current having a steady direct component upon which an alternating wave is superposed in such a manner that the resultant electromagnetic field set up by each of said windings is' substantially zero when the amplitude of said alternating wave is zero.

5. The method of electromagnetically controlling the defiection of a cathode ray beam which comprises setting up at each of two spaced positions between whichv the cathode ray beam may be deflected a plurality of component-magnetomotive forces each having a direct and alternating component and combinin said magnetometive forces to produce a resultant electromagnetic field having alternating components only, the direct component being substantially sup- Dressed.

6. The method of electromagnetically deflecting a cathode ray beam which comprisessetting up at each of two positions between which the cathode ray beam maybe deflected two opposed unidirectional magnetomotive forces, and varying said magnetomotive forces in opposite directions simultaneously to produce at each of said positions a resultant alternating magnetomotive force having substantially no steady component.

7. The method of supplying deflecting current from the output of a'push-pull amplifier having two electric discharge tubes to deflecting coils positioned on opposite sides of a cathode ray beam produced in a cathode ray tube, which comprises connecting difierent substantially equal portions of each of said coils in the output circuit of different tubes, respectively, so that the resultant magnetomotive force produced by each of said coils is substantially zero when equal currents flow through said portions, respectively, and applying deflecting potential in opposite phase to the input circuits of said tubes, respectively, to cause the magnetomotive forces set up by said portions, r

respectively, of each of said coils to chang in opposite directions simultaneously and thereby produce a resultant electromagnetic field for deflecting said cathode ray beam.

8. Apparatus for deflecting a cathode ray beam produced in a cathode ray tube comprising a pair of coils positioned on opposite sides, respectively, of said cathode ray beam, a push-pull amplifier comprising a .pair of electric discharge devices each having an anode, a cathode and a control electrode, means for connecting the opp site ends of each coil to said anodes, respectively, means for connecting a portion of each coil between its ends to the cathode of each of said electric discharge devices to complete the anode current circuit for each of said electric discharge devices, said anode current circuits including a source of anode current, and means for supplying to the control electrode-cathode circuits of said electrio discharge devices, respectively, varying electromotive forces which vary in opposite directions simultaneously.

9. In combination, means for generating a cath ode ray beam, a pair of coils positioned on or posite sides of said cathode ray beam for producing an electromagnetic field f or deilectingsaid cathode ray beam, a push-pull amplifier circuit comprising electric discharge means having a pair of anodes, a pair of control electrodes and a pair of cathodes, a common source of anode current connected between each of said cathodes and a terminal for each of said coils between its end terminals, means for connecting the end terminals of each of said coils to said anodes. reDectively, and means for impressing upon said control electrodes, respectively, with respect to said cathodes, varying deflecting potentials which are out of phase with respect to each other.

10.1in combination, means for generating a cathode ray beam, a pair of coils positioned on opposite sides of said cathode ray beam for producing an electromagnetic held for deflecting said cathode ray beam when suitably energized, a push-pull amplifier circuit comprising a pair of electric discharge devices each having a cathode,

.an anode and a control electrode, a common source of anode current connected between each of said cathodes and a mid-tap for each of said coils, means for connecting the ends of each of said coils to said anodes, respectively, to complete the anode-cathode circuit of each of said electric discharge devices, a-pair of condensers and a source of charging current therefor connected in series circuit, means in said circuit for maintaining the charging current substantially constant, means for periodically discharging said condensers, and means for impressing the alternating components of the voltages across said condensers between the control electrode and cathode of said electric discharge devices, respectively, to cause the anode current of one of said devic s o ch nge in one direction while the anode current of the other device simultaneously changes in the opposite direction.

11. In combination, means for generating a cathode ray beam, deflectin means comprising a pair of coils positioned on opposite sides of said cathode ray beam, respectively, for setting up an electromagnetic field for deflecting said cathode ray beam, a push-pull amplifier, and means ior supplying to said deflecting means from said pushpull amplifier varying electric energy for causing said coils to set up varying magnetomotive forces which are aiding and simultaneously substantially equal at any instant.

12,. In combination, a cathode ray tube having means for generating a cathode ray beam, two pairs of coils on opposite sides of said cathode ray tube for producing under control of energy supplied thereto an electric field for deflecting said cathode ray beam along a coordinate, and means for supplying to the coils, respectively, of each of said pairs of coils periodically varying currents of the same periodicity the amplitude of one of which is increasing while the amplitude of the other is simultaneously decreasing to cause to be set up by said pairs of coils, respectively, magnetomotive forces which aiding and by the coils, respectively, of each Pair component magnetomotive forces which are opposing.

13. In combination, a push pull amplifier, a cathode ray tube having means for generating a cathode ray beam, means for deflecting said beam along a first coordinate, means for deflecting said cathode ray beam along a second coordinate sub said cathode ray tube to be aiding, thereoy oaus- -ing the field intensity due to said magnetomotlve.

forces to be substantially uniform at any instant over the region through which said cathode ray 1 o beam s deflected along said first coordinate,

MILLARD w. BALDWIN, JR. 

